80 PORCELLANASTERIDAE. 



himself describes four new species in his relatively brief paper. But the omis- 

 sion is not serious for the present species is notably distinct and might well be 

 made the type of a new genus. It resembles S. chuni and S. paucispinus in 

 the large disk and short arms ; the general facies is thus very different from that 

 of the typical members of Styracaster. But the absence of paxillae and the 

 presence of only five narrow cribriform organs distinguishes monacanthus at 

 once from its two nearest alhes and these differences are accentuated by the 

 very low and wide interradial marginal plates and the presence of only a single 

 spine on the supramarginal series of plates of each arm. The low, rounded 

 scale-hke spines on the margin of the oral plates are an added featm-e worthy 

 of note. The disk is Ught gray and the arms and marginal plates are nearly 

 white, in shght contrast. 



Station 4701. Eastern Tropical Pacific, 19° 11' 30" S., 102° 24' W., 2,265 fms. Bott. temp. 35.5°. 

 Dk. br. choc, c, mang. nod. 



One specimen. 



styracaster paucispinus. 



Plate 2, fig. 3, 4. 

 Lttdwig, 1907. Zool. Anz,, 31, p. 315. 



Ludwig's description of this species is somewhat more ample than that of 

 monacanthus but as in the case of that species, he does not discuss its relation- 

 ships. It agrees with S. armatus, spinosus, and edwardsi in the possession of 

 only three cribriform organs in each interbrachial arc; in the great breadth of 

 these, paucispinus is nearest to armatus. But it differs very markedly from all 

 these species, in its very short arms, R equalling 2.5 r or less, whereas in the three 

 other species, R = 3r or more. Associated \vith this shortness of arms is a 

 reduction in the number of superomarginal spines which are never more than 

 three to an arm and may be one only; Ludwig says "two or three" but I faU to 

 find more than two in any case; the longest ones are scarcely 2 mm. high and 

 are quite thick at the base. The "winzigen, granuloiden stachelchen" on the 

 ventrolateral plates are so minute as to hardly warrant the name, and in one 

 specimen appear to be qxiite wanting. The adambulacral plates have a marked 

 depression or shallow furrow on the ventral surface; this runs from the inner 

 adoral corner of the plate, where it is deepest, to the outer aboral corner, where 

 it flattens out entirely. 



